Magnetism and local environment model in (Ni1-cCoc)0.78P0.14B0.08amorphous alloys

The magnetic properties of amorphous alloys (Ni
1-c
Co
c
)
0.78
P
0.14
B
0.08
have been investigated. The samples were prepared by the splat-cooling method. The Curie temperatures have been determined and the magnetization measurements performed for 1.7°K
\leq T \leq 270\deg
K and fields up to 70 kOe. Ni
0.78
P
0.14
B
0.08
is paramagnetic, whereas Co
0.78
P
0.14
B
0.08
is ferromagnetic until the crystallization temperature (678°K). The average moment per cobalt atom is
1.15 \mu_{B}
. In (Ni
1-c
Co
c
)
0.78
P
0.14
B
0.08
the critical concentration for the paramagnetic-ferromagnetic transition is
c \simeq 0.15
, this transition occurs in an inhomogeneous way. The saturation magnetization in the whole concentration range can be interpreted (as for some crystallized alloys and compounds) by a local environment model, when a reasonable short range order is assumed. In such a model the magnetic moment per cobalt atom is related merely to the number of its Co first neighbors n
Co
. For n
Co
=0 and 1 the cobalt atom is not magnetic, for n
Co
= 2 and 3 it carries a small moment
\mu_{1} = 0.50 \mu_{B}
and for n
Co
> 3 it is magnetic with
\mu_{2} = 1.15 \mu_{B}
as in Co
0.78
P
0.14
B
0.08
; the nickel atoms do not carry a substantial moment in the entire concentration range. These features are comparable to those obtained in some crystalline alloys.